dbus - Support desktop notifications via the StatusNotifier D-Bus service (used by most modern desktop environments).
debug - Enable extra debug codepaths, like asserts and extra output. If you want to get meaningful backtraces see https://wiki.gentoo.org/wiki/Project:Quality_Assurance/Backtraces
gui - Build the Qt5 GUI client for quassel. If this USE flag is disabled, the GUI is not built, and cannot be used. You might want to disable this on the server, but you need it enabled on the client.
kde - Add support for software made by KDE, a free software community
ldap - Add LDAP support (Lightweight Directory Access Protocol)
monolithic - Build standalone client with integrated core, no external quasselcore needed. Only useful if you don't want to use Quassel's client/server model. The server and X flags are not needed in this case but it is possible to enable them too.
oxygen - Support the Oxygen icon set that was the default for KDE4.
postgres - Add support for the postgresql database
server - Build the server binary. If this USE flag is disabled, the 'core' server binary for quassel is not built, and cannot be used. You need this enabled on the server, but you might want to disable it on the client.
